The present invention relates to an induction heating apparatus which may be used as a cooking device.
The induction heating apparatus generally comprises a static power converter for converting low frequency power into high frequency power and at least one coreless heater coil which is energized by the high frequency power. When the induction heating apparatus is used as a cooking device and is subjected to a load such as a cooking pan placed in the vicinity of the heater coil, the impedance of the circuit including the heater coil varies in a broad range depending upon the material forming the load. This results in serious fluctuations in the operating conditions of the heater coil and the converter. Such a tendency is pronounced during an incipient stage of operation of the apparatus and a condition in which the heater coil is subjected to an increased load. The fluctuations in the operating conditions of the converter and the heater coil are, furthermore, caused by an unusual change in the current or the voltage applied to the heater coil and, in the result, tend to invite burn-out of the heater coil and destroy insulating materials incorporated into the heating unit. Where the heating unit consists of a plurality of heater coils, the fluctuations of impedance are caused in the individual heater coils when one heater coil is subjected to a load with another heater coil kept unloaded or when the heater coils are subjected to different loads. The present invention contemplates elimination of such problems inherent in the induction heating apparatus.